Electrically-active implantable bio-medical devices (such as for example pacemakers, cochlear implants, and neural prosthetics) are increasing in popularity due to the potential of continuous monitoring, instantaneous and directed delivery of treatments, reduction of treatment costs, and unique treatment options. However, because many of the component materials used in such devices are not bio-compatible, that is, they are toxic to the body and can induce undesirable biological reactions, it is critical to hermetically seal the non-bio-compatible components (e.g. CMOS, passive components, batteries) in a bio-compatible material, so that the body does not have a cyto-toxic response. Hermetic sealing also helps protects electrical components from damage due to moisture and the corrosive environment in the body.
FIG. 1 shows a schematic illustration of a general approach to hermetically encapsulating implantable devices, such as 10, where non-bio-compatible components and materials 11, such as electronics, are encapsulated in a hermetically sealed package 12 made of bio-compatible materials. In this arrangement, an array of hermetic electrically conducting feedthroughs 13 is provided on an electrically insulating portion 14 of the package 12 for use as electrical conduits which allow communication of electrical signals between the body and electronics within the package.
And U.S. Pat. No. 7,881,799 describes a retinal prosthetic device having a hermetically sealed electronic package that contains a single side of the package that consists of electrical feedthroughs to transfer electrical signals between the device electronics and the polymer electrode array that attaches to the retina. One limitation of this assembly method is a restriction in the number of electrical signals that can be transmitted through the electronics package. State-of-the-art bio-compatible ceramics with electrical feedthroughs are limited in density by the inability to create closely spaced, small diameter vias that can be filled with metal paste.
In order to improve the performance of implantable devices, it is advantageous to provide electrically conductive feedthroughs which allow connection to hermetically sealed electronic devices from more than one wall of the hermetic package so as to increase feedthrough density and interactivity with the implanted medium.